Part 25

Shape.—Thin, flat sheet extending outward and upward, and then inward.

Relation.—Interiorly with the larynx.

Action.—The two muscles of this kind acting together, close the glottis by drawing the apices of the arytenoids to the median line.

=Thyreo-arytenoideus.= Location.—Supero-lateral portion of the superior larynx.

Origin.—From the entire outer margin of the thyroid plate and the outer margin of the cricoid bone.

Insertion.—All along the outer margin of the arytenoid bone and the outer border of the central cricoid piece.

Shape.—A thin, flat sheet.

Relations.—Infero-laterally with the superior larynx.

Action.—The two muscles of this kind acting together, open the glottis by pulling the arytenoid bone outward.

=Tracheo-lateralis= (Fig. 20, No. 2). Location.—Along the lateral side of the trachea.

Origin.—By the union of the bronchio-trachealis posticus and bronchio-trachealis anticus, on the lateral side of the trachea, about 1½ centimeters from the bifurcation of the trachea.

Insertion.—In delicate fan-like structure to the side of the trachea, near the superior larynx.

Shape.—Thin, ribbon-shaped, closely attached to the trachea.

Relations.—Internally with the trachea, and externally with the skin and other integument.

Action.—Acts as a brace to the sides of the trachea, and contracting, approximates the tracheal rings and thus shortens the trachea.

=Broncho-trachealis Posticus= (Fig. 21, No. 3). Location.—Postero-superior portion of the trachea. The fibers pass downward and backward.

Origin.—From the inferior end of the tracheo-lateralis.

Insertion.—To the end of the third half of the bronchial ring of the same side.

Shape.—A small fasciculus.

Relations.—Internally with the trachea, and externally with the skin and other integument.

FIG. 20.—The anterior pectoral region. 1, Sterno-trachealis. 2, Tracheo-lateralis. 3, Broncho-trachealis brevis. 4, Costal process of sternum. 5, Right and left carotid converging and occupying same sheath at 6. 7, The heart showing branches of coronary artery. 8, Cervical air-sac. 9, Left brachio-cephalic artery. 10, Right brachio-cephalic artery. 11, Trachea. 12, Inferior larynx. 13. Subclavian artery. 14, Carotid trunk. 15, Internal thoracic artery. 16 Thyroid gland. 17, Anterior vena cava. 18, Auricular appendage. ]

FIG. 21.—The inferior tracheal region. 1, Bronchialis anticus. 2, Bronchialis posticus. 3, Broncho-trachealis posticus. 4, Broncho-trachealis anticus. ]

Action.—A tensor of the true or inferior larynx.

=Broncho-trachealis Anticus= (Fig. 21, No. 4). Location.—Anterior portion of the inferior extremity of the trachea.

Origin.—The anterior branch of the bifurcated tracheo-lateralis.

Insertion.—To the anterior extremity of the third half ring of the bronchus of the same side.

Shape.—A small fasciculus.

Relations.—Internally with the trachea, and externally with the skin and other integument.